Controlled spalling utilizing vaporizable release layers

ABSTRACT

Method for a controlled spalling utilizing vaporizable release layers. For example, a method comprises providing a base substrate, depositing a stressor layer and a vaporizable release layer on the base substrate, forming a flexible support layer on at least one of the stressor layer and the vaporizable release layer, spalling an upper portion of the base substrate, securing the spalled upper portion of the base substrate to a handle substrate, and vaporizing the vaporizable release layer.

BACKGROUND

Controlled spalling technology now makes it possible to remove (“spall”)a thin (typically <100 micron or μm) substrate layer from the surface ofa base substrate with near-zero thickness-direction kerf losses, and todo this multiple times on the same base substrate. The potential costsavings are enormous since (i) the thickness of the spalled substratelayer can be limited to the thickness needed for the intended devicesand (ii) many substrate layers may be derived from a single wafer oringot.

However, the fragility of the spalled substrate layers typicallyrequires that they be supported by one or more handle substrates orflexible support layers for at least some stages of processing. Aflexible support layer (e.g., some type of tape) is typically firstbonded to the stressor layer side of a substrate wafer/stressor layercouple, leaving an overhang of tape which may be used to initiate spall.After spalling, an upper portion of the substrate and the stressor layerremain attached to the flexible support layer. After the desiredprocessing is completed on the exposed (spalled) surface of the spalledlayer, it is often desirable to mount the spalled layer on a permanenthandle substrate and remove the flexible support layer.

SUMMARY

Embodiments provide methods and apparatus for a controlled spallingutilizing vaporizable release layers. For example, in one embodiment, amethod comprises providing a base substrate, depositing a stressor layerand a vaporizable release layer on the base substrate, forming aflexible support layer on at least one of the stressor layer and thevaporizable release layer, spalling an upper portion of the basesubstrate, securing the spalled upper portion of the base substrate to ahandle substrate and vaporizing the vaporizable release layer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A illustrates a cross-sectional view of a structure comprising abase substrate to be spalled, according to an embodiment of theinvention.

FIG. 1B illustrates a cross-sectional view of a structure comprising abase substrate, a stressor layer and a vaporizable release layer formedon top of the base substrate, according to an embodiment of theinvention.

FIG. 1C illustrates a cross-sectional view of a structure comprising abase substrate, a stressor layer, a vaporizable release layer and aflexible handle formed on top of the vaporizable release layer,according to an embodiment of the invention.

FIG. 1D illustrates a cross-sectional view of the structure in FIG. 1Cafter spalling of the base substrate, according to an embodiment of theinvention.

FIG. 1E illustrates a cross-sectional view of a structure comprising aspalled portion of a base substrate after being bonded to a handlesubstrate, according to an embodiment of the invention.

FIG. 1F illustrates a cross-sectional view of a structure after removalof a vaporizable release layer, according to an embodiment of theinvention.

FIG. 2A shows a flexible support layer incorporating a vaporizablerelease layer, according to an embodiment of the invention.

FIG. 2B shows a flexible support layer comprising a vaporizable releaselayer and additional adhesive tape, according to an embodiment of theinvention.

FIG. 2C shows a flexible support layer comprising a vaporizable releaselayer formed between two layers of adhesive tape, according to anembodiment of the invention.

FIG. 3A illustrates a cross-sectional view of a structure comprising abase substrate to be spalled, according to an embodiment of theinvention.

FIG. 3B illustrates a cross-sectional view of a structure comprising abase substrate and a vaporizable release layer formed on top of the basesubstrate, according to an embodiment of the invention.

FIG. 3C illustrates a cross-sectional view of a structure comprising avaporizable release layer patterned to define a stressor layer edge,according to an embodiment of the invention.

FIG. 3D illustrates the cross-sectional view of the structure in FIG. 3Cafter deposition of a stressor layer, according to an embodiment of theinvention.

FIG. 3E illustrates the cross-sectional view of a structure showing astressor layer over a vaporizable release layer debonding after mildheating, according to an embodiment of the invention.

FIG. 4A illustrates a cross-sectional view of a structure comprising abase substrate to be spalled, according to an embodiment of theinvention.

FIG. 4B illustrates a cross-sectional view of a structure comprising abase substrate, a vaporizable release layer and a stressor layer formedon top of the base substrate, according to an embodiment of theinvention.

FIG. 4C illustrates a cross-sectional view of a structure comprising abase substrate, a vaporizable release layer, a stressor layer and aflexible handle formed on top of the vaporizable release layer,according to an embodiment of the invention.

FIG. 4D illustrates a cross-sectional view of the structure in FIG. 4Cafter spalling of the base substrate, according to an embodiment of theinvention.

FIG. 4E illustrates a cross-sectional view of a structure comprising aspalled portion of a base substrate after being bonded to a handlesubstrate, according to an embodiment of the invention.

FIG. 4F illustrates a cross-sectional view of a structure after removalof a vaporizable release layer, according to an embodiment of theinvention.

DETAILED DESCRIPTION

Embodiments will now be described in further detail with regard tocontrolled spalling techniques utilizing a vaporizable release layer. Itis to be understood that various layers, structures, and/or regionsshown in the accompanying drawings are schematic illustrations that arenot necessarily drawn to scale. In addition, for ease of explanation,one or more layers, structures, and regions of a type commonly used toform semiconductor devices or structures may not be explicitly shown ina given drawing. This does not imply that any of the layers, structures,and regions not explicitly shown are omitted from the actual devices.

Furthermore, it is to be understood that embodiments discussed hereinare not limited to the particular materials, features, and processingsteps shown and described herein. In particular, with respect toformation (fabricating or processing) steps, it is to be emphasized thatthe descriptions provided herein are not intended to encompass all ofthe steps that may be used to form a functional integrated circuitdevice. Rather, certain steps that are commonly used in forming suchdevices, such as, for example, but not limited to, wet cleaning andannealing steps, are purposefully not described herein for economy ofdescription.

Moreover, the same or similar reference numbers are used throughout thedrawings to denote the same or similar features, elements, layers,regions, or structures, and thus, a detailed explanation of the same orsimilar features, elements, layers, regions, or structures will not berepeated for each of the drawings. It is to be understood that the terms“about” or “substantially” as used herein with regard to thicknesses,widths, percentages, ranges, etc., are meant to denote being close orapproximate to, but not exactly. For example, the term “about” or“substantially” as used herein implies that a small margin of error ispresent such as, by way of example, 1% or less than the stated amount.Also, in the figures, the illustrated scale of one layer, structure,and/or region relative to another layer, structure, and/or region is notnecessarily intended to represent actual scale.

It can be difficult to find a flexible support layer (or flexiblesupport layer stack) that has all of the following properties: (i) thinand flexible enough not to interfere with the spalling process, (ii)adherent enough to remain bonded during the processing for which itshould stay on, and (iii) detachable enough to be removed withoutdamaging the spalled layer when the flexible support is no longer needed(e.g., after the spalled layer has been bonded to a handle substrate).

Three existing flexible support layers in use all have drawbacks. Whilethermal release tapes (e.g., Nitto Denko tapes comprising a polyesterbacking layer and a thermal release layer composed of an adhesiveembedded with small particles that irreversibly expand upon heating) arereleasable with near-zero force, existing formulations of these tapeshave a thickness (typically 75 μm for the adhesive and 100 μm or morefor the backing) and rigidity that reduces the effectiveness of thestressor layer and interferes with good spalling. UV-release tapes(comprising a backing layer and a UV-degradable adhesive) are thinenough not to interfere with spalling, but are still tacky after UVtreatment and require a prohibitive amount of force to release. VariousKapton polyimide tapes have the desired flexibility and thermalstability, but are difficult to remove cleanly and selectively tounderlying layers.

A number of different illustrative embodiments for improving a spallingprocess by utilizing vaporizable release layers will be described belowwith reference to FIGS. 1A through 4F. Each of the figures illustratesteps which may be used in the process of spalling a base substrate.

The term “vaporizable release layer” refers to a layer composed ofmaterials that lose physical integrity upon heating. Vaporizable releaselayers are distinguished from above-mentioned thermal release layers inthat thermal release layers typically contain microcapsules that expandupon heating whereas vaporizable release layers give off some type ofgas. For example, a class of materials known as norbornenes (developedby BFGoodrich and marketed by Promerus under the trademarked nameUnity®) provide for a suitable vaporizable release layer. Monomericnorbornene, for example, is a low molecular weight bridged cyclichydrocarbon (C₇H₁₀) that can be functionalized and/or polymerized toform materials that cleanly decompose into high volatility products uponheating at temperatures in the range 200-300° C. The norbornene materialcan be used for temporary wafer bonding and can be applied using astandard spin coat process. A simple thermal process can be used torelease the wafer leaving little material residue.

Embodiments of the present invention are however, not necessarilylimited to using norbornenes as the vaporizable release layer, butrather, any class of suitable materials that lose physical integrityupon heating can be utilized for the methods and apparatus discussedherein. For example, metals with low melting points (In, Ga, Sn etc.),waxes, or any material that is adherent at deposition temperature andcondition but non-adherent at elevated temperatures, may be utilizedwithout departing from the scope or spirit of the invention.

Referring now to FIGS. 1A-1F, an embodiment for a controlled spallingprocess is illustrated wherein a base substrate is spalled, the spalledlayer of the base substrate is transferred to a handle substrate and aflexible support layer is released by the vaporizable release layer.FIG. 1A illustrates a structure 100 comprising a base substrate 101. Thebase substrate 101 may be, but is not limited to, a semiconductor waferor ingot comprising an inorganic single crystal or polycrystallinematerial such as Ge, Si, GaAs, sapphire, GaN or any solid brittlematerial. In FIG. 1B, a structure 110 comprises a stressor layer 102 anda vaporizable release layer 103 deposited onto the top surface of thebase substrate 101. The stressor layer 102 may comprise, for example,Ni, Cr, Fe, and the like, and may additionally comprise other metals andalloys, such as Ti, to improve its adhesive properties. The vaporizablerelease layer 103 may comprise, for example, but not limited to,norbornene materials. In FIG. 1C, a structure 120 comprises the basesubstrate 101, the stressor layer 102, the vaporizable release layer 103and a flexible support layer 104 comprising flexible support tape 105and a tape adhesive 106 formed on top of the vaporizable release layer103. The flexible support tape 105 may comprise, for example, a Kaptontape or a Vinyl tape.

FIG. 1D illustrates a structure 130 wherein the base substrate 101 hasbeen spalled leaving an upper spalled portion 101-A of the basesubstrate 101 attached to the stressor layer 102. The characteristics ofthe stressor layer 102, such as thickness and stress, and the flexiblesupport layer 104 are adjusted to create a fracture in the basesubstrate 101 that ultimately separates the upper spalled portion 101-Afrom the base substrate 101. The remaining lower portion of the basesubstrate 101 may be, for example, utilized for further spalling or maybe recycled for further processing. The upper spalled portion 101-Aremains attached to the stressor layer 102, the vaporizable releaselayer 103 and the flexible support layer 104. FIG. 1E illustrates astructure 140 wherein the upper spalled portion 101-A, along with thestressor layer 102, the vaporizable release layer 103 and the flexiblesupport layer 104, has been transferred to a handle substrate 107. Anepoxy layer 108 is provided between the bottom surface of the upperspalled portion 101-A and the top surface of the handle substrate 107 inorder to attach the upper spalled portion 101-A to the handle substrate107, utilizing heated laminating force 109. Then, a simple thermalprocess is utilized to raise the temperature of the structure 140 to200-300 degrees Celsius resulting in a structure 150 shown in FIG. 1F,whereupon the vaporizable release layer 103 has been vaporized releasingthe flexible support layer 104 from the stressor layer 102. Lastly, thestressor layer 102 is etched away leaving only the thin spalled layer101-A.

In the above embodiment, for ease of processing, the vaporizable releaselayer 103 may be incorporated into the flexible support layer 104, asshown in FIG. 2A. The vaporizable release layer 103 may be pre-coatedonto the flexible support layer 104 by including it as one or morelayers of a multilayer flexible support structure. The vaporizablerelease layer 103 may be formed on surfaces by spinning or spraying froma solution. However, the vaporizable release layer 103 may not besufficiently adhesive to bond to the stressor layer 102 (not shown inFIG. 2A). Therefore, any additional tape adhesive may be utilized toincrease the bond strength between the vaporizable release layer 103 andthe stressor layer 102, as shown in FIGS. 2B and 2C. In FIG. 2B, a layerof tape adhesive 201 is deposited below the vaporizable release layer103. Alternatively, in FIG. 2C, the vaporizable release layer 103 isdeposited between a first layer of tape adhesive 202 and a second layerof tape adhesive 203. In embodiments utilizing the additional tapeadhesive as shown in FIGS. 2B and 2C, an adhesive residue may be left onthe stressor layer 102 (not shown in FIG. 2B or 2C) after vaporizing thevaporizable release layer 103.

In another embodiment of the invention, a patterned layer of aphotoimageable vaporizable release layer is used to define a stressorlayer edge. This is typically used for edge exclusion to facilitate thespalling initiation. Stressor layer regions over the vaporizable releaselayer regions will debond from the substrate upon mild heating. FIGS.3A-3E show the steps of this embodiment in more detail. After thestressor layer edge definition step, the process may continue on to thenext steps, such as the processes shown in FIGS. 1B-1F.

FIG. 3A illustrates a structure 300 comprising a base substrate 301. InFIG. 3B, a structure 310 shows a vaporizable release layer 303 depositedonto the top surface of the base substrate 301. In FIG. 3C, a structure320 shows the vaporizable release layer 303 patterned to define astressor layer edge. In FIG. 3D, a structure 330 shows a stressor layer302 deposited on the base substrate 301 and on the vaporizable releaselayer 303 patterned to define the stressor layer edge. After applyingmild heating (preferably a temperature ranging from 50 degrees Celsiusto 400 degrees Celsius), the stressor layer 302 debonds from thevaporizable release layer 303 defining the stressor layer edge, as shownin structure 340 in FIG. 3E. Thereafter, the structure 340 may furtherbe processed for controlled spalling via steps discussed with referencesto FIGS. 1B-1F (i.e., depositing a layer of a vaporizable release layer,depositing the flexible support layer, etc.).

In yet another embodiment of the invention, a vaporizable release layeris used to remove a stressor layer from a spalled layer of a basesubstrate. FIGS. 4A-4F illustrate a controlled spalling process whereina base substrate is spalled, the spalled layer of the base substrate istransferred to a handle substrate and a stressor layer is released by avaporizable release layer.

FIG. 4A illustrates a structure 400 comprising a base substrate 401. InFIG. 4B, a structure 410 comprises a vaporizable release layer 403deposited onto the top surface of the base substrate 401, and a stressorlayer 402 deposited onto the vaporizable release layer 403. In FIG. 4C,a structure 420 comprises the base substrate 401, the vaporizablerelease layer 403, the stressor layer 402 and a flexible support layer404 comprising flexible support tape 405 and a tape adhesive 406 formedon top of the stressor layer 402. FIG. 4D illustrates a structure 430wherein the base substrate 401 has been spalled leaving an upper spalledportion 401-A of the base substrate 401. The remaining lower portion ofthe base substrate 401 may be, for example, utilized for furtherspalling or may be recycled for further processing. The upper spalledportion 401-A remains attached to the vaporizable release layer 403, thestressor layer 402 and the flexible support layer 404. FIG. 4Eillustrates a structure 440 wherein the upper spalled portion 401-A,along with the vaporizable release layer 403, the stressor layer 402 andthe flexible support layer 404, has been transferred to a handlesubstrate 407. An epoxy layer 408 is provided between the bottom surfaceof the upper spalled portion 401-A and the top surface of the handlesubstrate 407 in order to attach the upper spalled portion 401-A to thehandle substrate 407, utilizing heated laminating force 409. Then, asimple thermal process is utilized to raise the temperature of thestructure 440 to 200-300 degrees Celsius resulting in a structure 450shown in FIG. 4F, whereupon the vaporizable release layer 403 has beenvaporized releasing the stressor layer 402 from the upper spalledportion 401-A. In this configuration, no further etching is necessary.

Although illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that theinvention is not limited to those precise embodiments, and that variousother changes and modifications may be made by one skilled in artwithout departing from the scope or spirit of the invention.

What is claimed is:
 1. A method, comprising the steps of: providing abase substrate; depositing a stressor layer and a vaporizable releaselayer on the base substrate, wherein the vaporizable release layercomprises norbornene materials which vaporize at a temperature rangingfrom about 200 degrees Celsius to about 300 degrees Celsius; forming aflexible support layer on at least one of the stressor layer and thevaporizable release layer; spalling an upper portion of the basesubstrate; securing the spalled upper portion of the base substrate to ahandle substrate; and vaporizing the vaporizable release layer.
 2. Themethod of claim 1, wherein the vaporizable release layer is positionedbetween the stressor layer and the flexible support layer.
 3. The methodof claim 1, wherein the vaporizable release layer is positioned betweenthe stressor layer and the base substrate.
 4. The method of claim 1,wherein the vaporizable release layer is patterned to define edges ofthe stressor layer and is positioned between the stressor layer and thebase substrate.
 5. The method of claim 1, wherein the flexible supportlayer comprises at least one of a flexible support tape and a tapeadhesive.
 6. The method of claim 1, wherein the vaporizable releaselayer is applied via a standard spin coat process.
 7. A method,comprising the steps of: providing a base substrate; depositing astressor layer and a vaporizable release layer on the base substrate;forming a flexible support layer on at least one of the stressor layerand the vaporizable release layer, wherein the flexible support layercomprises at least one of a flexible support tape and a tape adhesive,and wherein the vaporizable release layer is pre-coated onto theflexible support layer; spalling an upper portion of the base substrate;securing the spalled upper portion of the base substrate to a handlesubstrate; and vaporizing the vaporizable release layer.
 8. Anapparatus, comprising: a base substrate; a stressor layer and avaporizable release layer formed on the base substrate, wherein thevaporizable release layer comprises norbornene materials which vaporizeat a temperature ranging from about 200 degrees Celsius to about 300degrees Celsius; and a flexible support layer formed on at least one ofthe stressor layer and the vaporizable release layer; wherein theapparatus is configured to enable an upper portion of the base substrateto be spalled and secured to a handle substrate, and the vaporizablerelease layer to be vaporized.
 9. The apparatus of claim 8, wherein thevaporizable release layer is positioned between the stressor layer andthe flexible support layer.
 10. The apparatus of claim 8, wherein thevaporizable release layer is positioned between the stressor layer andthe base substrate.
 11. The apparatus of claim 8, wherein thevaporizable release layer is patterned to define edges of the stressorlayer and is positioned between the stressor layer and the basesubstrate.
 12. The apparatus of claim 8, wherein the flexible supportlayer comprises at least one of a flexible support tape and a tapeadhesive.
 13. The apparatus of claim 12, wherein the vaporizable releaselayer is pre-coated onto the flexible support layer.
 14. The apparatusof claim 8, wherein the vaporizable release layer is applied via astandard spin coat process.
 15. A method for spalling a base substrate,comprising the steps of: providing the base substrate; depositing avaporizable release layer on the base substrate; depositing a stressorlayer on the vaporizable release layer; forming a flexible support layeron the stressor layer, wherein the flexible support layer comprises atleast one of a flexible support tape and a tape adhesive, and whereinthe vaporizable release layer is pre-coated onto the flexible supportlayer; spalling an upper portion of the base substrate; securing thespalled upper portion of the base substrate to a handle substrate; andvaporizing the vaporizable release layer.
 16. The method of claim 15,wherein the vaporizable release layer is patterned to define edges ofthe stressor layer.